Methysergide blocks the sleep suppressant action of quipazine in rats

Drug-induced activation of the inferior olivary nucleus in young rabbits. Differential effects of harmaline and quipazine

Ontogenic evolution of behavioural and electrophysiological responses to the serotonergic agents, quipazine and harmaline, was studied in the maturing rabbit in normal and pretreated conditions. As regards behavioural effects, tremor induced by quipazine was present from the first postnatal day and was antagonized by methysergide, but not by p-chlorophenylalanine (PCPA) or pretreatment with 5,7-dihydroxytryptamine (5,7-DHT). In contrast, tremor induced by harmaline could not be elicited before the second postnatal week and was partially antagonized by methysergide and 5,7-DHT, but not by PCPA. Electrophysiological studies of cell activity in the inferior olivary nucleus revealed a similar dependency on age since rhythmic activation of the inferior olivary nucleus could be registered from the first postnatal day with quipazine and only from the 8th postnatal day with harmaline; drug interactions with methysergide, PCPA and 5,7-DHT were the same as for the behavioural observations. It is suggested that quipazine directly activates serotonin receptors which are already present at birth, whereas harmaline requires the presence of serotonergic fibres for such activation.

Quipazine has a biphasic effect on slow wave sleep and reduces REM sleep rebound in REM sleep deprived rats

Rats implanted with electrodes for polygraphic recording were deprived of REM sleep for 24 hr. Following REM sleep deprivation animals were injected with quipazine maleate (7.5 mg/kg IP) and were polygraphically recorded for 48 hr. The results show that quipazine reduces REM sleep rebound and that it has a biphasic effect on slow-wave sleep: initial 6 hr suppression is followed by a delayed increase in the second 24 hr recording period. The initial suppression of slow-wave sleep we attribute to the stimulation of central serotonergic receptors while the effect on REM sleep rebound may result from quipazine's action on central catecholamines.